—— compared with the value the total tissue dose rate as is measured by the Tissue Equie- vaient Chamber and this means that the Tissue Equivalent Chamber is a measure of the valid~ ity or the measure of the integrity of our values. The Ionization Chambers are primary stray radiation measurement instruments, they are little affected, althouch to some extent but they are little affected by RF pickup end do sudden variations in the radiation field. It 142 true.that they may not be saturated for large instantaneous dose rates, but this can be tested for, simply by varying the collecting potential across the ionization chamber, We plan in the future to calibrate these instruments over a wider range of ener gies than heretofore. One big difficulty in the use of these ionization chambers is the weight of the electrometers which we require, The ionization currents are pro- duced at about ten to the minus thirteen It ie therefore necessary to uce | anperes. 104